1. Field of the Invention
The present invention relates to molding machines for molding articles by injecting molding material under pressure into an article-defining mold cavity defined by separated and cooperating mold portions. More particularly, the invention relates to a molding machine that incorporates hydraulically operated drive arrangements for performing various of the functions of the machine, and that includes an hydraulic clamping cylinder for holding the mold portions together during material injection, the hydraulic fluid for which clamping cylinder is maintained in a separate reservoir that is spaced from and in communication with a main hydraulic reservoir.
2. Description of the Related Art
In machines for molding parts from a flowable material that is introduced into a mold cavity under pressure, particularly plastics injection molding machines, where the various structures for performing rotary and translatory movements are hydraulically operated, the normal practice is to provide a main reservoir for the hydraulic fluid, and to position that main reservoir above a large capacity hydralic cylinder that provides a clamping force for holding together mold portions during the injection of the molding material. However, as the parts to be molded increase in size, the clamping cylinder must, of necessity, increase as well in order to provide the necessary additional clamping force to hold together the larger mold portions during the material injection step. During injection, the material to be molded is injected into the mold cavity under very high pressure, which results in very high forces within the mold cavity and that act on the respective mold portions to tend to separate them. Accordingly, very high clamping forces are necessary in order to overcome the higher separation forces that exist during the injection operation.
As the molding machines increase in clamping capacity, the hydraulic cylinders for providing the necessary clamping force also increase in size, which, in turn, requires an hydraulic reservoir of correspondingly greater size. Consequently, as the machine size increases, along with the size of the hydraulic reservoir, the machines attain a height of such a magnitude that the machines cannot be accommodated in relatively low-ceilinged structures, thereby requiring expensive high bay facilities in order to accommodate such machines.
Accordingly, it is an object of the present invention to provide an improved, high clamping force capacity molding machine wherein the overall height of the machine is maintained at a reasonably low level.
It is a further object of the present invention to provide a molding machine having a separate reservoir for the hydraulic fluid that is used to operate the clamping cylinder.
It is a still further object of the present invention to provide a molding machine in which the hydraulic fluid for operating the clamping system is contained in a reservoir that includes overflow protection to permit overflow to occur into a main reservoir that is separate from the clamping system reservoir.